1. Field of the Invention
The present invention relates to a chrominance signal processing apparatus for recording and reproducing chrominance signals of the color television signals in a color video tape recorder (color VTR). The chrominance signal processing apparatus carries out frequency conversion of a low band converted chrominance signal or carrier chrominance signal, jitter correction of the carrier-frequency, signal level correction, black-and-white signal discrimination of input video signal and prohibition of the chrominance signal during recording and reproduction.
2. Description of the Prior Art
Conventional commercial color VTRs employ a recording system called a "color under" system in which the carrier chrominance signal which is converted to a low-band signal is recorded on a video tape under an FM luminance signal band by means of frequency multiplex system. The FM luminance signal is demodulated during playback, while the low-band converted original chrominance signal of the high color subcarrier frequency. The thus obtained two signals are added so as to thereby obtain a reproduced color television signal. Various circuit systems are conventionally proposed for integrating the circuits used in the chrominance signal processing apparatus. (e.g. I. Nakagawa, A. Shibata, and N. Horie, "New chrominance signal processing LSI," IEEE Transactions on Consumer Electronics, Vol. 26, No. 3, pp. 315-322, 1980). A typical configuration example of the conventional chrominance signal processing apparatus is shown in FIG. 1 and will hereafter be explained.
In FIG. 1, the carrier chrominance signal of a carrier-frequency f sc (3.58 M Hz in the case of an NTSC system) is fed from the terminal 1 during recording, and adjusted to an adequate level by an ACC amplifier (ACC) 2 and supplied to one input of the frequency converter 3. To the other input of the frequency modulator 3 is fed the carrier of a frequency f sc+f c which is the sum of the low-band converted carrier frequency fc (629 K Hz in the case of a VTR of a VHS system) and the carrier-frequency f sc of the carrier chrominance signal.
The level adjusted carrier chrominance signal and the carrier of the frequency f sc+f c are multipliid by the frequency converter 3. The low-band converted chrominance signal of the carrier-frequency fc obtained as a result of the multiplication is extracted by the lowpass filter (LPF) 4, and supplied to the killer switch (KILLER SW) 7 through the recording/reproducing output switch 6. The control terminal of the killer switch 7 is supplied with the discriminating results of the presence of the chrominance signal, by which the low-band converted chrominance signal from the switch 6 is switched so as to be supplied to the output terminal 8.
During playback, the low-band converted chrominance signal of the carrier-frequency fc is fed from the terminal 1 to be level adjusted by ACC amplifier 2 and supplied to one input of the frequency converter 3. To the other input of the frequency converter 3 is supplied the carrier of the frequency of f sc+fc which is the sum of the carrier-frequency fc of the low-band converter chrominance signal from the terminal 1 and the reference color subcarrier frequency f sc for reproduced carrier chrominance signal. The level adjusted low-band converted chrominance signal and the carrier of frequency f sc+fc are multiplied by the frequency converter 3. The carrier chrominance signal of the reference carrier-frequency f sc is obtained as a result of the multiplication and is extracted by the bandpass filter (BPF) 5, and outputted to the terminal 8 through the switch 6 and the killer switch 7.
The killer switch is controlled by the discriminating results of the presence of the chrominance signal as in the case of recording.
In the recording and playback system as described above, the ACC operation for adjusting the level of the carrier chrominance signal or the low-band converted chrominance signal by the ACC amplifier 2, the APC operation for providing the jitter of the same phase for the carrier of the frequency f sc+fc supplied to said frequency converter 3 according to the jitter of the phase of the carrier of the carrier chrominance signal or the low-band converted chrominance signal, and the color killer operation to determine whether the carrier chrominance signal of the low-band converted chrominance signal is inputted from the terminal 1 and prohibit the signal output to the terminal 8 when the chrominance signal is not present are carried out.
These operations are conventionally carried out in the following method.
In the first place, during recording, from the carrier chrominance signal which is passed by the ACC amplifier 2, and, during reproduction, from the reproduced carrier chrominance signal converted of the frequency after passing the bandpass filter 5, the burst portion is extracted by the burst gate (BG) 10.
During both recording and reproduction in the ACC operation, the peak level of the extracted burst portion is detected by the ACC detected (ACC DET) 11. The direct current (DC) portion is extracted by the lowpass filter (LPF) 12, and is supplied to the ACC amplifier 2 as the signal used for gain control. The ACC amplifier 2, if the signal DC voltage for gain control is high, i.e., the level of the burst portion is large, operates in a direction to decrease the gain, and if the signal DC voltage is low, the ACC amplifier 2 operates in a direction to increase the gain so that the level of the chrominance signal is kept constant due to the above-mentioned feed-back loop.
During recording in the APC operation, the signal generator (VXO) 13 functions as the voltage control oscillator to oscillate at the color subcarrier frequency f sc. This oscillation output and the burst portion obtained by the burst gate 10 are synchronously detected by the phase comparator (PC), and the results of which are fed back to the frequency control input of the signal generator 13 through the lowpass filter (LPF) 15 and the switch 16. Thus, the signal generator 13 performs the synchronous detection using the phase comparator 14 and oscillates at a frequency so that the signal passed through the lowpass filter 15 becomes equal to 0.
The oscillation output of the signal generator 13 turns into the color subcarrier frequency which is synchronized by the phase difference between the extracted burst portion and 90.degree. and is supplied to one input of the frequency converter 17. The other input is supplied with the low-band converter carrier. To generate the low-band converted carrier, a signal of a frequency nfH multiplied by n (n is a positive integer) of the frequency fH of the horizontal synchronous signal inputted from the terminal 23 is generated during the recording by the phase locked loop (hereinafter PLL) consisting of the phase comparator (PC) 18, lowpass filter (LPF) 19, switch 20, signal generator 21, and 1/n divider (1/n) 22. The generated signal is divided by the carrier generator circuit (PS/PI) 24 and it phase is shifted by 90.degree. (hereafter PC process) per one horizontal interval in an opposite direction with respect to each track based on the recorded track discriminating signal PG inputted from the terminal 25. Or the phase is inverted (hereafter PI process) per one horizontal interval of every other track. The frequency fc is 40 fH and is shifted by 90.degree. per one horizontal interval when an NTSC television signal is recorded by a VHS system.
For recording, the chrominance subcarrier of the frequency f sc and the low-band converted carrier of the frequency fc are multiplied by the frequency converter 17, and a signal of the frequency f sc sc+fc is extracted by the bandpass filter (BPF) 26. The extracted signal is supplied to the frequency converter 3, whereby the low-band converted carrier of the low-band converted chrominance signal to be outputted from the terminal 8 and the low-band converted chrominance signal generated by the carrier generator circuit 24 are synchronized. For reproduction, since the signal generator 13 becomes a reference oscillaor to generate the color subcarrier frequency of the reference frequency f sc because the signal generator circuit 13 is frequency controlled by the constant voltage supplied from the reference voltage circuit (REF) 27 through the switch 16. The output of the phase comparator 14 is supplied to the signal generator 21 through the lowpass filter 15 and switch 20, whereby the signal generating circuit 21 operates so that the frequency converted burst of the reproduced carrier chrominance signal to be ouputted from the terminal 8 is synchronized with the reference color subcarrier generated by the signal generator 13.
With regard to the color killer operation, because the burst taken out from the burst gate 10 has a 90.degree. phase difference during both recording and playback due to the APC operation for the color subcarrier frequency from the signal generator 13, the carrier with the same phase as the burst is produced by shifting the phase of the color subcarrier frequency from the signal generator 13 90.degree. using the 90.degree. phase shifter (90.degree. SHIFT) 28. The carrier is supplied to the killer detector (KILLER DET) 29 for synchronous detection of the taken-out burst. The comparator (COMP) 29 determines the presence of the chrominance signal by the DC voltage after it has passed through the lowpass filter (LPF) 30, and the control signal is supplied to the killer switch 7.
In the chrominance signal processing apparatus of a conventional example as above, three detection circuits are necessary to perform the operations of the ACC, APC and color killer. They are the ACC detector 11 for peak level detection of the burst, the comparator circuit 14 for synchronous detection of the color subcarrier frequency from the burst and signal generator 13, and the killer detector 29 for synchronous detection of 90.degree. phase shifted color subcarrier frequency from the signal generator 13 as well as the burst. Because these circuits are complicated and of large scale in order to achieve respectively specified characteristics and because the performance of the respective operations are determined by the characteristics of the detection circuits and the analog lowpass filter of the subsequent stages, it is difficult to establish the circuit constant. The conventional chrominance signal processing apparatus has a further disadvantage due to the increased number of externally added parts.